The Histology &Imaging Core will provide a central site and umbrella authority, which together with satellite infrastructure on this campus confers necessary services, instrumentation, supervision and training for PPG members and personnel within their laboratories. The Core's two major functions are (i) to assist characterization of undifferentiated and differentiated phenotypes of mouse and human embryonic stem cells and their derivatives (all Subprojects), and (2) to assist with the unambiguous histologic characterization of engrafted and regenerated myocardium following stem cell transplantation (Subprojects 1, 3, 4). To achieve these goals the core will assume a training and advisory role while providing services including fixation, embedding and sectioning;routine, histochemical and immunohistochemical staining;widefield and fluorescence microscopy;laser-scanning confocal and multi-photon microscopy;electron microscopy; microangiography. By maintaining an organized online database, processing of images to reconstruct and qualitatively analyze the extent of stem cell engraftment in transplanted myocardium will be provided.